Low-viscosity channel flow, originating from a melt-weakened mid-crustal layer, is one of the most popular tectonic models to explain the exhumation of deep-seated rocks in the Greater Himalayan Sequence (GHS). The driving mechanism of such channel flow, generally attributed to focused erosion in the mountain front, is still debated, and yet to be resolved. Moreover, the channel flow model cannot explain eclogites in the GHS. In this study, we present a new two-dimensional thermo-mechanical numerical model, based on lubrication dynamics to demonstrate the exhumation process of deep crustal rocks in GHS. The model suggests that a dynamic-pressure drop in the Himalayan wedge, following a large reduction in the India-Asia convergence velocity (15 cm/yr at 50 Ma to nearly 5 cm/yr at ∼22 Ma) localized a fully developed extrusion zone, which controlled the pressure-temperature-time (P-T-t) path of GHS rocks. We show that the wedge extrusion, originated in the lower crust (∼60 km), was initially bounded by two oppositely directed ductile shear zones: the South Tibetan Detachment systems (STDS) at the top and the Higher Himalayan Discontinuity (HHD) at the bottom. With time the bottom shear boundary of the extrusion zone underwent a southward migration, forming the Main Central Thrust (MCT) at ∼17 Ma. Our model successfully reproduces two apparently major paradoxical observations in the Himalaya: syn-convergence extension and inverted metamorphic isograds. Model peak P (10–17 kb) and T (700–820°C) and the exhumation P-T-t path estimated from several Lagrangian points, traveling through the extrusion zone, are largely compatible with the petrological observations in the GHS. The model results account for the observed asymmetric P-T distribution between the MCT and STDS, showing peak P-T values close to the MCT. The lubrication dynamics proposed in this article sheds light on the fast exhumation event (>1 cm/yr) in the most active phase of crustal extrusion (22-17 Ma), followed by a slowed-down event. Finally, our model explains why the extrusion zone became weak in the last 8-10 Ma in the history of India-Asia collision.

低粘度通道流起源于融化弱的中地壳层，是解释大喜马拉雅层序（GHS）中深部岩石掘出的最受欢迎的构造模型之一。这种通道流的驱动机制通常归因于山前的集中侵蚀，目前仍在争论中，尚待解决。此外，渠道流模型无法解释GHS中的榴辉岩。在这项研究中，我们基于润滑动力学提出了一个新的二维热机械数值模型，以证明GHS中深层地壳的挖掘过程。该模型表明，随着印度-亚洲收敛速度的大幅降低（50 Ma处的15 cm / yr到约22 Ma处的近5 cm / yr），喜马拉雅山楔的动压下降使一个完全发达的挤出带局部化。 ，P--t）GHS岩石的路径。我们显示楔形挤压起源于下地壳（〜60 km），最初由两个相反方向的韧性剪切带界定：顶部的南藏分离系（STDS）和高度的喜马拉雅间断性（HHD）。底部。随着时间的推移，挤压带的底部剪切边界经历了向南偏移，形成了约17 Ma的主中心推力（MCT）。我们的模型成功地再现了喜马拉雅山中两个明显的主要矛盾现象：同收敛扩展和倒置变质等梯度。模型峰P （10–17 kb）和 Ť （700–820°C）和发掘 P--Ť--Ť从拉格朗日几个点估计的，经过挤压带的路径与全球统一制度中的岩石学观测结果基本相符。模型结果说明了观察到的不对称P--Ť MCT和STDS之间的分布，显示峰值 PT值接近MCT。本文提出的润滑动力学揭示了地壳挤压最活跃阶段（22-17 Ma）中的快速发掘事件（> 1 cm / yr），随后是减速事件。最后，我们的模型解释了为什么在印度-亚洲碰撞的历史中，挤压带在最后的8-10 Ma变得脆弱。